1. Field of the Invention
The present invention relates to a non-invasive method and device for locating and mapping nerves and nerve bundles by electro-stimulation. More particularly, the present invention relates to a method and device for locating and mapping the cavernosal nerve bundle by electro-stimulation to assist in safe and effective implantation of radioactive seeds for prostate brachytherapy or to enhance any other non-invasive or minimally invasive form of prostate cancer therapy.
2. Related Art
Many methods of therapy are available to treat localized prostate cancer Such methods include, but are not limited to, radical prostatectomy, modifiedradical prostatectomy, external beam radiation therapy (EBRT), brachytherapy, cryotherapy, hormonal therapy, and careful observation of the gland. Successful prostate cancer therapy results in the removal or destruction of cancerous prostate tissue without injury to the nerves or tissue associated with the surrounding anatomy, particularly, the cavernosal nerve associated with penile tumescence or the urethral anatomy.
One minimally invasive method of therapy, prostate brachytherapy, involves the implantation of radioactive seeds in an area proximate to cancerous prostate tissue, but sufficiently distant from healthy prostate tissue. The radioactive seeds are implanted in the prostate by a seed delivery needle or applicator which is passed through the patient""s perineum and into the prostate. Although in practice since 1913, prostate brachytherapy has recently gained popularity in light of patient dissatisfaction with radical and modified-radical prostatectomies (particularly, loss of penile tumescence (impotency) and urethral complications) and the minimally invasive nature of prostate brachytherapy.
While prostate brachytherapy qualifies as a minimally invasive method of therapy, the nerves and tissue of the surrounding anatomy are susceptible to injury since the brachytherapist cannot visualize the same. For example, if the tip of the seed delivery needle contacts or pierces the cavemosal nerve bundle, function of the nerve could be irreparably impaired, resulting perhaps in impotency. In addition, if the radioactive seeds of the brachytherapy method are positioned too close to the cavernosal nerve bundle, the seeds could destroy the cavernosal nerve fibers, again resulting in impotence or related complications. For such reasons, care should be exercised when selecting implantation sites and routes of delivery for the radioactive seeds of prostate brachytherapy.
The success of prostate brachytherapy can be improved if the brachytherapist refers to a guide or map of the diseased prostate to select safe and effective seed implantation sites and routes of delivery. With xe2x80x9cpre-planxe2x80x9d brachytherapy, a measurement of the patient""s prostate is taken several weeks prior to implantation of the radioactive seeds. Based on those measurements, the brachytherapist plots seed implantation coordinates on a grid or template which corresponds to the height and width of the prostate. While pre-plan guided brachytherapy facilitates implantation of radioactive seeds, it fails to provide any information on location of the cavemosal nerve bundle to avoid contact with the seed delivery needle (mechanical nerve injury) or unnecessary exposure to the radioactive material of the seeds (radiational nerve injury). In addition, pre-plan guided brachytherapy cannot account for changes in the size or shape of the prostate subsequent to the measurements taken weeks prior.
CT-guided brachytherapy, developed by the Memorial Sloan Kettering Cancer Center, relies on images generated by computed tomography to yield a computer-programmed plan of radioactive seed implantation. Although CT-guided brachytherapy provides more detailed information on the size, shape and vascular structure of the prostate gland, it cannot determine the exact location of the cavemosal nerve bundle to reduce mechanical or radiational injury.
Transrectal ultrasound brachytherapy relies on volume studies to determine the size and shape of the diseased prostate. Coordinates for the proper implantation of radioactive seeds are based on the volume study information and plotted on a pre-plan grid. To implant the radioactive seeds, the brachytherapist advances a radioactive seed delivery needle into the prostate through coordinates plotted on a grid positioned proximate the perineum. The coordinates plotted on the perineal grid correspond to the coordinates plotted on the pre-plan grid mentioned above. As the brachytherapist advances the seed delivery needle through the perineal grid and into the prostate, an image of the advancing seed delivery needle appears on the monitor of the transrectal ultrasound. When the seed delivery needle has reached the proper position interior of the prostate, the brachytherapist deposits and implants the radioactive seeds in the cancerous tissue of the prostate.
Some brachytherapists combine transrectal ultrasound with fluoroscopy to provide a three-dimensional transperineal image of the prostate. While either method provides a real time three-dimensional image of the prostate and its vascular structure, it too lacks the ability to effectively locate and map the cavernosal nerve bundle to avoid unintended contact with a seed delivery needle or radioactive seed which could result in mechanical or radiational damage.
Since brachytherapists (and clinicians practicing others forms of non-invasive or minimally invasive prostate cancer therapy) operate xe2x80x9cblindlyxe2x80x9d with respect to the cavernosal nerve bundle (i.e., no surgical exposure or open visualization of the nerve bundle), a need exists for a device which locates and maps the cavernosal nerve bundle prior to application of brachytherapy to avoid mechanical or radiational injury to the nerve.
Devices for locating a nerve for delivery of anesthesia by needle or syringe are disclosed in U.S. Pat. No. 4,515,168 to Chester et al. and U.S. Pat. No. 3,682,162 to Colyer. While the mentioned patents use electro-stimulation to indicate needle position relative to the nerve, such devices rely heavily on the skill of the clinician and fail to account for the complex and delayed response patterns of autonomic nerves, such as the cavernosal nerve. See, e.g., p. 2 of the ""501 application incorporated herein by reference.
In U.S. Pat. Nos. 5,284,153 and 5,284,154, Raymond et al. disclose a device and method to locate and protect a nerve from intra-operative injury. More particularly, the device has been configured to identify, locate and protect the cavernosal nerve while excising cancerous prostate tissue (i.e., radical or modified-radical prostatectomy). The device comprises an instrument for applying a stimulus to tissue in the area of the cavernosal nerve, a tumescence response detector, means for evaluating the detected response, means for modifying the stimulus intensity, and means for indicating the proximity of the instrument to the cavernosal nerve. Successful location of the nerve, however, appears to depend on the clinician""s ability to effectively advance the stimulating instrument through the body tissue to locate the nerve. In addition, the tip of the stimulating instrument (i.e., the probe) appears more suitable for invasive therapies, such as radical or modified-radical prostatectomy, rather than a minimally invasive therapy, such as brachytherapy.
In an attempt to reduce reliance on the skill of the clinician, Raymond et al. developed a closed-loop system for locating the cavernosal nerve for radical prostatectomy. The apparatus of U.S. Pat. No. 5,775,331 (the ""331 patent) comprises a stimulating probe having an array of electrodes, an automatic control means, and a tumescence response detector. Using the electrode array of the stimulating probe, a clinician applies a stimulus to an area of tissue believed to contain the cavernosal nerve. The response detecting means records a tumescence response, if any, and the control means automatically modifies activation of the electrode array (i.e., subsequent sites of stimulation) based on an evaluation of the response to prior stimulation. The steps are repeated until the nerve has been located.
Like the prior device to Raymond et al., the apparatus of the ""331 patent comprises a probe structure better suited for invasive prostate cancer therapy methods, such as radical prostatectomy.
Subsequent to development of the device disclosed in the ""331 patent, Raymond et al. realized that other factors associated with the patient or the clinical environment (e.g., the patient""s blood pressure, inadvertent manipulation of the response detector, or the amount of anesthesia administered to the patient) could evoke a change in tumescence. See pp. 3-4 of the ""501 application. The method and device of the ""501 application seeks to avoid a misinterpretation of tumescence by assessing the xe2x80x9cstabilityxe2x80x9d or xe2x80x9cunstabilityxe2x80x9d of the response signal prior to an attempt to locate the nerve by electro-stimulation. To assess the stability of the tumescence signal, the device of the ""501 application compares the tumescence signal (prior to application of electro-stimulation) to a library of stored reference values which correspond to a state of stability or unstability. If the tumescence signal has been characterized as unstable, the device waits for the tumescence signal to stabilize (or for an over-ride command) before proceeding with electro-stimulation.
The device of the ""501 application effectively addresses the complex factors associated with stimulation of the cavernosal nerve to avoid the misinterpretation of tumescence response signals which results in inaccurate or delayed locating of the cavernosal nerve.
In light of the many considerations discussed above, the need exists for a device which accurately locates and maps the cavernosal nerve bundle to facilitate application of invasive, minimally invasive, and non-invasive methods of therapy for prostate cancer.
Another need exists for a device which assesses the stability of the tumescence signal prior to any attempt to locate the cavernosal nerve by electro-stimulation to avoid misinterpretation of any change in the tumescence signal evoked by unrelated factors associated with the patient or clinical field, rather than by electro-stimulation.
A further need exists for a device for mapping and locating the cavemosal nerve bundle to reduce or avoid injury associated with minimally invasive or non-invasive (blind) methods of prostate cancer therapy (e.g., mechanical nerve injury resulting from direct contact with seed implantation needles or radiational nerve injury resulting from exposure to radioactive seeds implanted in the prostate and intended to destroy only cancerous prostate tissue).
Yet another need exists for a device which locates and maps the cavernosal nerve bundle and which mates with conventional equipment for applying known methods of prostate cancer therapy (e.g., radioactive seed implantation needles, cryotherapy needles, or pre-loaded seed cartridges).
Still another need exists for a device which can store information on the size and shape of the prostate, past therapy application sites, and the location of the cavernosal nerve bundle for future therapy applications.
It was with the preceding needs in mind that the present invention was developed. The present invention represents a modification and improvement to the Method and Device for Locating a Nerve disclosed and claimed in the ""501 application. It comprises a method and device for locating and mapping the cavemosal nerve bundle by electro-stimulation to enable safe and effective implantation of radioactive seeds for prostate brachytherapy. By locating and mapping the cavernosal nerve bundle prior to seed implantation, the brachytherapist can make intra-operative decisions to avoid mechanical and radiational injury to the nerve which results in impotency or other prostate-Urethral complications. The device of the invention takes the form of an automated closed-looped electro-stimulating system having a handle for manipulating the device, a stimulating tip for applying an electro-stimulus to a tissue site, a control unit to activate and terminate application of the electro-stimulus and to interpret a tumescence response, a sensor for detecting and measuring a tumescence response, a patient ground return, and a display monitor to indicate the nature, stability and strength of the tumescence response to the brachytherapist. If the control unit concludes that the applied electro-stimulus failed to evoke a tumescence response in excess of a pre-determined baseline and that the tissue lacks cavemosal nerve bundle fibers, radioactive seeds can be implanted in the prostate through the stimulating tip which also serves as a brachytherapy seed implantation needle.
In another embodiment of the invention, a kit for locating and mapping a nerve to avoid injuring the nerve during application of therapy has been provided. The kit comprises a device for locating the nerve using electro-stimulation and a grid for mapping coordinates corresponding to tissue sites. The device for comprises means for detecting and measuring a response signal and a change in the response signal evoked by application of an electro-stimulus to the nerve, means for analyzing the response signal provided by said detecting and measuring means to determine its stability, means for applying an electro-stimulus to an area of tissue, and means for interpreting a change in the signal evoked by application of the electro-stimulus to the nerve to the determine the location of the nerve. The means for applying the electro-stimulus to the tissue comprises a removable array of electrodes to determine the location of the nerve in an effort to avoid the nerve during the excision of tissue associated with radical prostatectomy. In another embodiment, the means for applying an electro-stimulus to the tissue comprises a removable needle for applying an electro-stimulus to the tissue area and for administering minimally invasive prostate cancer therapy through the perineum of the patient. The needle comprises a brachytherapy seed implantation needle. In another embodiment, the needle comprises a cryosurgery needle. The response detecting and measuring means comprises distensible fluid filled tubing.
A method for locating and mapping cavemosal nerve fibers to avoid injuring the nerve fibers during application of prostate cancer therapies has been provided, as well. The method comprises the steps of detecting and measuring a tumescence response signal from the cavemosal nerve, determining the stability of the tumescence response signal and characterizing it as stable or unstable, applying an electro-stimulus to a tissue site believed to contain the cavernosal nerve fibers if the tumescence response signal has been characterized as stable, detecting and measuring any change in the tumescence response signal evoked by application of the electro-stimulus, interpreting any change in the tumescence response signal evoked by application of the electro-stimulus, and determining if the tissue site contains cavernosal nerve fibers. The method further comprises the step of applying prostate cancer therapy to the tissue site it has been determined that the tissue site lacks cavemosal nerve fibers.